Aluminum (Al) is widely known to inhibit root growth: however, the exact mechanism of root growth inhibition is uncertain. To address the effect of Al on some components of the culture cycle, we used two Coffea arabica cell lines, L2 (Al-sensitive) and LAMt (Al-tolerant), and evaluated [3H]-thymidine incorporation into DNA and cyclin dependent kinase type A (CDKA) activity. We used cell cultures of the 7th day that were incubated with AlCl3 (100 μM) during different periods of time and observed a decrease of 47% in the rate of [3H]-thymidine incorporation into DNA when the cells were incubated in the presence of Al in the L2 cell line as compared with the LAMt cell line, which showed an increase of 150% over the control. A 1,132 bp cDNA for CDKA was amplified from C. arabica cells using real-time polymerase chain reaction (RT-PCR) and 3′-RACE, which encoded a 294 amino acid polypeptide. Incubation of the cells with AlCl3 (100 μM) causes inhibition of CDKA activity up to 72% in the L2 cell line but it was stimulated up to 70% in the LAMt cell line. The Al effect on expression of CDKA transcripts estimated by RT-PCR showed no effect upon AlCl3 incubation between the two cell lines. Our results suggest that Al affects cell cycle elements differentially in the two tested cell lines.